Abstract. It is shown that the phase angle of the third harmonic of polarization response

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The dielectric response of hard (Fe-doped) and soft (Nb-doped) rhombohedral Pb(Zr 0.58 Ti 0.42 ) 1-x Me x O 3 (PZT; Me= Fe or Nb) ceramics was studied at subswitching conditions over a wide range of temperatures (50°C to 450 °C) and frequencies (10 mHz to 10 kHz). The results show qualitative differences in behavior of the acceptor and donor doped samples. Hard materials exhibit a steep increase of the complex permittivity with decreasing frequency. The onset of the dispersion is thermally activated with activation energy of about 0.6-0.8 eV and is attributed here to oxygen vacancy hopping. Activation energy for ac conductivity observed in soft materials is estimated to about 1.7 eV, corresponding to the half of the energy gap of Pb(Zr,Ti)O 3 and is thus consistent with electronic conduction. The relevance of ionic hopping conductivity in hard materials to ferroelectric aging / deaging and hardening is analyzed. Strongionic conductivity in hard and its absence in soft samples agree well with the dipolar mechanism of ageing in hard materials and the absence of significant ageing in soft materials.

Technology, NO-7491 Trondheim,Highly dense and phase-pure ferroelectric ceramics in the (1-x)Bi0.5K0.5TiO3 -xBiFeO3 system have been prepared and examined in a wide range of composition (0.1 ≤ x ≤ 0.9). The dielectric and electromechanical properties have been shown to reach a maximum value at x ≈ 0.25 demonstrating a high strain performance (250 -370 pm/V in the temperature range 25 -175 °C).Stability of the strain response with respect to temperature, as well as frequency and amplitude of the driving electric field is reported and discussed.Perovskite ceramics based on mixed bismuth and alkali A-cations form a group of prominent lead-free piezoelectric alternatives whose potential is not fully explored yet.

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Four compounds of the Bi 4 Ti 3 O 12 /BiFeO 3 system with the formula Bi 2 Bi nϪ1 (Ti,Fe) n O 3nϩ3 , n ϭ 3, 4, 4.5 and 6 were studied using high-temperature X-ray powder diffraction and differential thermoanalysis methods. The crystal structure of the n ϭ 6 phase was refined by the Rietveld method. An unusual behaviour of thermal expansion attributed to an orthorhombic-to-tetragonal transformation was revealed. For all the compounds, the lattice parameter c vs temperature T dependence has three regions in the range of T ϭ 20 Ϫ750°C interpreted as (1) expansion of the initial orthorhombic phase, (2) a pronounced structure reconstruction to the tetragonal phase, (3) an expansion of the tetragonal phase. 1603The crystal structure of Bi 7 Ti 3 Fe 3 O 21 based on 6-layer-perovskite blocks is proposed from X-ray powder diffraction data. The Rietveld refinement of the structure in the orthorhombic space group F2mm with lattice parameters a ϭ 5.4699(3), b ϭ 5.4924(3), c ϭ 57.551(3) Å (R p ϭ 9.4, R wp ϭ 11.9, R exp ϭ 4.7, R B ϭ 4.4 %) shows that a distorted 6-layer model fits the data of Bi 7 Ti 3 Fe 3 O 21 .

Here, we report on a giant dielectric relaxation in (1-x)Bi 0.5 K 0.5 TiO 3-xBiFeO 3 ceramics below ~300 °C, which becomes more pronounced with increasing BiFeO 3 content. The relaxation was shown to be of Maxwell-Wagner type and associated with charge depletion at the electroded interfaces. It was also shown that the relaxation could be controlled or, eventually, could be removed by heat treatment in controlled partial pressure of oxygen. This was rationalized by the relationship between the electrical conductivity and variation in the oxidation state of Fe, which is strongly coupled to the partial pressure of oxygen. The results are discussed with emphasis on oxygen diffusion and point defect equilibria involving oxygen vacancies and iron in divalent and tetravalent state. Finally, the barrier-free dielectric properties of the (1-x)Bi 0.5 K 0.5 TiO 3-xBiFeO 3 ceramics are reported.